The invention disclosed herein is a die for accurately sizing the bullet receiving neck of a pistol or rifle ammunition case and for aligning the neck coaxial with the body of the case.
The most widely used method of reloading ammunition cases involves sizing the entire case to the dimensions it had when it was originally manufactured. This is intended to assure that reclaimed ammunition cases will be completely interchangeable between any gun chamber made to standard dimensions. An accurate fit of a reclaimed case in a gun chamber is frequently more important than interchangeability to competitive shooters because they will be using a single gun in competition. Skilled marksmen have long known the most accurate ammunition case is reloaded by sizing only the neck of the case to hold the bullet. This leaves the rest of the cartridge "fire-formed" to fit perfectly in the chamber of the particular gun in which it was formed. Accurate sizing is usually done by pushing the case into a die which sizes the neck smaller than desired without affecting the body of the case. Then an expander is either pulled or pushed through the neck of the case to leave the neck about 0.001" smaller than the bullet to obtain a press fit.
The reason for undersizing the neck and then expanding it to the correct size is to compensate for cartridge case thickness variations. If every case had exactly the same wall thickness, it would be possible to simply push the case into a die of the correct size for a perfect fit. However, cases vary because of manufacturing tolerances and the forces generated by repeated use.
A problem with prior art sizing methods is that concentricity and axial misalignment between the neck and body of the case can be caused by using existing standard dies. The centerline of the neck axis to the centerline of the case head can frequently be offset by as much as 0.025". Thus, the bullet can be not only seated off center in the case neck but its axis can also be at an angle with the axis of the body of the case. The lack of concentricity and presence of axial misalignment both affect shooting accuracy adversely.
A further problem of undersizing the neck and then expanding it up to proper size is that it shortens the case life caused by the extra working of the brass out of which the case is made.
U.S. Pat. No. 4,133,249, issued Jan. 9, 1979, discloses an ammunition case reloading press in which one approach to sizing the neck of the case and obtaining concentricity and alignment between the neck and body of rifle and pistol ammunition cases is demonstrated. The patent also provides for resizing the metal ferrule on shotgun shells. The resizer devices are built into the press and a substantial amount of mechanism is dedicated to doing the neck and body resizing of a case. The approach is to mount a case in such manner that it can be disposed within a collet. The collet is basically conventional in that it is composed of a plurality of fingers arranged in a circle with space between them so they can be driven radially inwardly to press against the outside of the case neck and body while a cylindrical mandrel is positioned inside of the case. The collet fingers are connected at one end and they are springy so that the collet tends to spring open to allow insertion of an ammunition case. The collet is arranged for being drawn into a cylinder. As the collet fingers are drawn into the cylinder, the cylinder wall presses the collet fingers radially inward to squeeze the wall of the case body against the mandrel. The mandrel also has a tip which drives the spent primer out of the case. The problem with this arrangement is that the collet type sizer has to be designed for fitting in only one press so all of the advantages of sizing with traditional standard dies that will fit into the presses of practically all manufacturers, are lost.